Since I dont know honestly here I a diagram of 120/208 with b phase 208 to g/n
There is where we got disconnected from you.
Thus is called 120/240 three phase four with, with a 208V high leg.
You do not mention the 208 when naming it because there will normally never be a load from high leg to ground.
You can have 240V single phase loads between any two ungrounded lines, 240V three phase loads in delta only, and 120V lighting loads from A or C to Neutral.
If some of the lights are working and some are not, you have most likely lost B and either A or C.
To measure POCO feed, open all main and load breakers and use a low impedance meter or Wiggy to measure line to line and line to neutral.
If the voltages to ground are weird with a low impedance meter, then you may have lost the POCO neutral.